Charging voltage measuring device for substrate and ion beam irradiating device

ABSTRACT

The charging voltage measuring device includes a measuring electrode for forming an electrostatic capacity Cs with a substrate disposed on a substrate holding unit, a measuring capacitor, which has an electrostatic capacity Cm, being connected between the measuring electrode and a ground potential portion, and, a voltage measuring unit for measuring a measuring voltage Vm across the measuring capacitor, and a calculating unit. The calculating unit  22  calculates the charging voltage Vs on the surface of the substrate at time t1 in accordance with the following numerical expression on the basis of the measuring voltage Vm(t1) at time t1, an inverse K of a voltage dividing ratio and a resistance value Rm of a resistor disposed in parallel to the measuring capacitor  18,  when the measurement time is t1.  
       Vs=K[Vm ( t 1)+{1/( Cm·Rm )}∫ 0   t1   Vm ( t ) dt]   
     where K=(Cs+Cm)/Cs or K=Cm/Cs (if Cm&gt;&gt;Cs)

FIELD OF THE INVENTION

[0001] The present invention to a charging voltage measuring device andan ion beam irradiating device having a charging voltage measuringdevice which is employed in a process or apparatus for making ionimplantation, ion doping or plasma treatment on a substrate, or aprocess or apparatus for conveying or drying the substrate, in whichthere is a fear that the surface of the substrate is electrified.

Description of the Related Art

[0002] Referring to FIGS. 1 and 2, a related-art typical chargingvoltage measuring method employing no electrostatic chuck will bedescribed below by way of example.

[0003] First of all, when a substrate 6 is treated, a measuringelectrode 8 is not provided, the substrate 6 to be treated is held andsecured on a substrate holding unit 4 by a damper (not shown), andirradiated with an ion beam 2. In this way, the substrate 6 is treatedwith the ion implantation and ion doping.

[0004] The substrate holding unit 4 is a metallic plate, for example.The substrate 6 is a glass substrate for liquid crystal display, forexample, but may be a semiconductor substrate or the like.

[0005] If the ion beam 2 is applied onto the substrate 6, the surface ofthe substrate 6 is electrified (charged up) due to positive charges ofions in the ion beam 2. Especially when the substrate 6 has aninsulating property (electrical insulating property), the surface of thesubstrate 6 is more likely to be electrified. The glass substrate andthe semiconductor substrate having an insulating layer on the surfaceare exemplary. At this time, the charging voltage on the substratesurface is simply decided by the balance between ions radiated as theion beam 2 and electrons supplied to the substrate 6 along with the ionbeam 2. The electrons may be those in a plasma existing around the ionbeam 2 or those being supplied from an electron supply source as will bedescribed later.

[0006] In order to measure the charging voltage on the surface of thesubstrate 6 as above described, a metallic measuring electrode 8 wasplaced closely on the surface of the substrate 6, and the ion beam 2 wasapplied onto the measuring electrode to measure the voltage of themeasuring electrode 8 by a voltmeter 10, whereby the measured voltagewas regarded as the charging voltage on the substrate surface. When thesubstrate 6 was actually treated by applying the ion beam 2 thereto, themeasuring electrode 6 as an obstacle was removed.

[0007] With the related-art measuring method as above described, it isrequired to place the measuring electrode 8 on the surface of thesubstrate 6, whereby the charging voltage on the surface of thesubstrate 6 can not be measured during the actual treatment (e.g., ionimplantation).

[0008] Also, in measuring the charging voltage, the ion beam 2 isapplied onto the metallic measuring electrode 8, whereby the chargingvoltage on the substrate surface is not correctly measured due to adifference in the material between the surface of the substrate 6 andthe surface of the measuring electrode 8.

SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to provide a devicecapable of accurately measuring the charging voltage on the substratesurface that is actually treated.

[0010] According to a first aspect of the invention, there is providedwith a charging voltage measuring apparatus for measuring a chargingvoltage Vs on the surface of a substrate on a substrate holding unit,including:

[0011] a measuring electrode, for forming an electrostatic capacity Cswith said substrate, being disposed on said substrate holding unit tomake contact with or proximate to the back face of said held substrate,and said measuring electrode being electrically insulated from saidsubstrate holding unit;

[0012] a measuring capacitor connected between said measuring electrodeand a ground potential portion, said measuring capacitor having anelectrostatic capacity Cm;

[0013] a voltage measuring unit for measuring a measuring voltage Vmbetween both ends of said measuring capacitor; and a calculating unitfor calculating said charging voltage Vs in accordance with a followingnumerical expression 1 or its mathematically equivalent numericalexpression on the basis of an inverse K of a voltage dividing ratio thatis defined by the relation of said electrostatic capacities Cs and Cmand said measuring voltage Vm.

Vs=K·Vm  [Numerical expression 1]

[0014] where K=(Cs+Cm)/Cs or K=Cm/Cs (if Cm>>Cs)

[0015] This numerical expression 1 is the same as that of claim 1.

[0016] In this charging voltage measuring device according to the firstaspect of the present invention, the two electrostatic capacities Cs andCm are connected in series with each other, so that the charging voltageVs on the substrate surface during the treatment that is divided at thevoltage dividing ratio defined by the relation between the twoelectrostatic capacities Cs and Cm appears across the measuringcapacitor. This voltage is measured as the measuring voltage by thevoltmeter.

[0017] Accordingly, the charging voltage on the substrate surface duringthe actual treatment can be accurately obtained from the measuredvoltage Vm by multiplying the measuring voltage by the inverse K of thevoltage dividing ratio as indicated in the numerical expression 1.

[0018] According to the second aspect of the invention, there isprovided with a charging voltage measuring device apparatus formeasuring a charging voltage Vs on the surface of a substrate held on asubstrate holding unit, including:

[0019] a measuring electrode, for forming an electrostatic capacity Cswith said substrate, being disposed on said substrate holding unit tomake contact with or proximate to the back face of said held substrate,and said measuring electrode being electrically insulated from saidsubstrate holding unit;

[0020] a measuring capacitor connected between said measuring electrodeand a ground potential portion, said measuring capacitor having anelectrostatic capacity Cm;

[0021] a voltage measuring unit for measuring a measuring voltage Vmbetween both ends of said measuring capacitor; and

[0022] a calculator calculating unit for calculating said chargingvoltage Vs at time t1 in accordance with a following numericalexpression 2 or its mathematically equivalent numerical expression onthe basis of an inverse K of a voltage dividing ratio that is defined bythe relation between said electrostatic capacities Cs and Cm, and saidmeasuring voltage Vm(t1) at time t1, and a resistance value Rm of aresistor including an internal resistor of said voltmeter and disposedin parallel to said measuring capacitor, when the time is t, themeasurement start time is t=0, and the measurement time is t1.

Vs=K[Vm(t1)+{1/(Cm×Rm)}ò0t1Vm(t)dt][Numerical expression 2]

[0023] where K=(Cs+Cm)/Cs or K=Cm/Cs (if Cm>>Cs)

[0024] The numerical expression 2 is the same as that of claim 2.

Vs K[Vm(t1)+{1/(Cm·Rm)}∫₀ ^(t1) Vm(t)dt][Numerical expression 2]

[0025] where K=(Cs+Cm)/Cs or K=Cm/Cs (if Cm>>Cs)

[0026] A portion of the first term multiplied by K within the largebrackets in the numerical expression 2 has the almost same content as inthe numerical expression 1.

[0027] The second term within the large brackets in the numericalexpression 2 is provided for correcting for an amount of charges on thesubstrate surface leaking into the ground potential portion through theresistor in parallel to the measuring capacitor during the measurementby converting it into the voltage. The voltage in the second term isobtained across the measuring capacitor, and converted into the voltageon the surface of the substrate by multiplying the second term by K. Inthis way, correcting the voltage for an error due to charges leaking outvia the internal resistance in the voltmeter, the charging voltage Vs onthe substrate surface during the actual treatment is accuratelymeasured.

[0028] According to the third aspect of the invention, there is providedwith an ion beam irradiating apparatus for irradiating an ion beam ontoa substrate held on a substrate holding unit, including:

[0029] an plasma generating source for generating and supplyingelectrons to said substrate to suppress the electrification on thesurface of said substrate caused by irradiating said ion beam;

[0030] a charging voltage measuring device for the substrate accordingto the first or second aspect of the invention; and

[0031] a control unit for controlling an amount of electrons generatedfrom said electron supply source on the basis of charging voltage Vsmeasured by said charging voltage measuring device;

[0032] wherein said control unit controls to maintain said amount ofsaid electrons generated from said electron supply source when saidcharging voltage Vs is within a reference voltage range,

[0033] wherein said control unit controls to increase said amount ofsaid electrons generated from said electron supply source when saidcharging voltage Vs is higher than said reference voltage range, and

[0034] wherein said control unit controls to decrease said amount ofsaid electrons generated from said electron supply source when saidcharging voltage Vs is lower than said reference voltage range.

[0035] Since this ion beam irradiating device has the charging voltagemeasuring device according to first or second aspect of the invention,the charging voltage Vs on the substrate surface during the actualtreatment is accurately measured.

[0036] Additionally, the controller makes the feedback control for theelectron discharge source to automatically control the charging voltageVs on the substrate surface during the treatment to fall within thereference voltage range.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037]FIG. 1 is a diagram showing a charging voltage measuring deviceaccording to one embodiment of the present invention;

[0038]FIG. 2 is an equivalent circuit diagram around a measuringcapacitor in FIG. 1;

[0039]FIG. 3 is a view showing a charging voltage measuring deviceaccording to another embodiment of the invention;

[0040]FIG. 4 is an equivalent circuit diagram around a measuringcapacitor in FIG. 3;

[0041]FIG. 5 is a plan view showing one example of planar shape for thesubstrate holding unit, the substrate and the measuring electrode;

[0042]FIG. 6 is a diagram showing one example of a method for acquiringan inverse of voltage dividing ratio;

[0043]FIG. 7 is a schematic cross-sectional view showing an ion beamirradiating device according to one embodiment of this invention;

[0044]FIG. 8 is a block diagram showing a specific example of acontroller in FIG. 7;

[0045]FIG. 9 is a plan view showing one example of planar shape for thesubstrate holding unit, the substrate and the measuring electrode alongwith the ion beam;

[0046]FIG. 10 is a plan view showing another example of a measuringelectrode;

[0047]FIG. 11 is a plan view showing a further example of the measuringelectrode; and

[0048]FIG. 12 is a view showing one example of the related-art chargingvoltage measuring method.

DETAILED DESCRIPTION OF THE INVENTION

[0049]FIG. 1 is a diagram showing a charging voltage measuring deviceaccording to one embodiment of the present invention. FIG. 2 is anequivalent circuit diagram around a measuring capacitor in FIG. 1. Thesame or like parts are designated by the same numerals as in therelated-art example of FIG. 12, and the different points from therelated-art example will be mainly described below.

[0050] This charging voltage measuring device 12 includes a measuringelectrode 14, a measuring capacitor 18, a voltage measuring unit and acalculating unit. In this embodiment, the voltage measuring and thecalculating units are a voltmeter 20 and the calculator 22,respectively.

[0051] The measuring electrode 14 is disposed between a substrateholding unit 4 and a substrate 6. The substrate 6 is held on themeasuring electrode 14. The measuring electrode 14 is disposed on thesubstrate holding unit 4 (i.e., on a substrate holding face of thesubstrate holding unit 4) to make contact with or proximate to the backface of the substrate 6 held thereon, and electrically insulated fromthe substrate holding unit 4 to form an electrostatic capacity Cs withthe substrate 6.

[0052] The measuring electrode 14 is a plate-like (particularly, a thinplate-like) conductor (i.e., a conductive plate), The measuringelectrode 14 is covered with a thin insulating layer 16, including boththe upper and lower faces thereof in this embodiment. The substrate 6 isheld and secured on this insulating layer. Accordingly, the measuringelectrode 14 is located proximate to the back face of the substrate 6via the insulating layer 16. Usually, the substrate 6 is held andsecured by securing unit such as a clamper, not shown. The damper is notshown in the drawings.

[0053] Since the substrate holding unit 4 is made of a conductor such asa metal, the insulating layer 16 is also provided between the substrateholding unit 4 and the measuring electrode 14 in this example. However,if at least the surface of the substrate holding unit 4 is an insulatingmaterial, it is unnecessary to provide the insulating layer 16 betweenthe substrate holding unit 4 and the measuring electrode 14. This isbecause the potential of the measuring electrode 14 is taken out, evenif there is no insulating layer 16. The substrate holding unit 4 iselectrically connected to a ground potential portion in this embodiment.

[0054] Also, when the substrate 6 is made of an insulating material likea glass, there is no need for providing the insulating layer 16 betweenthe substrate 6 and the measuring electrode 14. This is because anelectrostatic capacity Cs is formed between the substrate 6 and themeasuring electrode 14, even if the insulating layer 16 is not provided.In this case, the measuring electrode 14 makes contact with the backface of the substrate 6. When the substrate 6 is electricallyconductive, the insulating layer 16 may be provided between thesubstrate 6 and the measuring electrode 14.

[0055] More specifically, the measuring electrode 14 made of an aluminumfoil, which is laminated with the insulating layer 16. The insulatinglayer 16 is made of polyethylene. The measuring electrode 14 is bondedon the substrate holding unit 4 in this embodiment. Since such measuringelectrode 14 can be very thin as a whole, there is an excellent thermalconductivity between the substrate 6 and the substrate holding unit 4,which is advantageous for efficiently cooling the substrate via thesubstrate holding unit 4 during the treatment. The substrate holdingunit 4 is cooled by refrigerant such as the cooling water to cool thesubstrate 6 efficiently in this embodiment.

[0056]FIG. 5 shows one example of a planar shape for the substrateholding unit 4, the substrate 6 and the measuring electrode 14. In thisexample, the measuring electrode 14 is slightly smaller than thesubstrate 6 to prevent an ion beam 2 from being applied on top of themeasuring electrode 14 without being intercepted by the substrate 6.However, the planar shape is not limited to this example (e.g., seeFIGS. 10 and 11).

[0057] The ion beam 2 may have a large area to cover the entiresubstrate 6, or may have a rectangular section as shown in FIG. 9, whenmechanically scanning the substrate holding unit 4 and the substrate 6,as shown in FIG. 7. Other shapes maybe employed.

[0058] Turning back to FIG. 1, the measuring capacitor 18 is connectedbetween the measuring electrode 14 and the ground potential portion. Letits electrostatic capacity be Cm. The ground potential portion is avacuum vessel (e.g., a vacuum vessel 30 in FIG. 7) for storing andtreating the substrate holding unit 4, for example.

[0059] The voltmeter 20 is connected across the measuring capacitor 18to measure the measuring voltage Vm that is a voltage across themeasuring capacitor 18.

[0060] The calculator 22 calculates the charging voltage Vs on thesurface of the substrate 6 being treated in accordance with thenumerical expression 3, on the basis of the inverse K of the voltagedividing ratio that is defined by the measuring voltage Vm measured bythe voltmeter 20 and the electrostatic capacities Cs and Cm.

[0061] Explaining in more detail, in this charging voltage measuringdevice 12, two electrostatic capacities Cs and Cm are connected inseries between the substrate 6 and the ground potential portion, so thatthe charging voltage Vs on the surface of the substrate 6 being treatedthat is divided at a voltage dividing ratio defined by the relationbetween the two electrostatic capacities Cs and Cm (which is obtained bythe well known method) appears across the measuring capacitor 18, asshown in FIG. 2. This voltage is measured as the measuring voltage Vm bythe voltmeter 20. Herein, the internal resistor of the voltmeter 20 issufficiently large and ignored.

[0062] Accordingly, the charging voltage Vs on the substrate surfaceduring the actual treatment can be accurately calculated from themeasuring voltage Vm by multiplying the measuring voltage Vm by theinverse K of the voltage dividing ratio, as indicated in the numericalexpression 3. This calculator 22 makes the calculation.

[0063] The measuring voltage Vm measured by the voltmeter 20 includesthe polarity ± and the magnitude, and therefore the charging voltage Vscalculated in the above way by the calculator 22 includes the polarity ±and the magnitude. The same is true with the charging voltage measuringdevice 12 as shown in FIG. 3.

[0064] The inverse K of the voltage dividing ratio is correctlyrepresented by the following numerical expression 5. When Cm>>Cs (e.g.,Cm is about 100 to 10000 times Cs), the numerical expression 6 may bealternatively employed without having great influence on the measuringaccuracy.

K=(Cs+Cm)/Cs[Numerical expression 3]

K=Cm/Cs[Numerical expression 4]

[0065] The value of K may be calculated within the calculator 22, or bymay be calculated in other ways and set in the calculator 22, wherebythe calculator 22 makes the calculation in accordance with the numericalexpression 1 or 2. Thereby, the arithmetical operation of the calculator22 is simplified. The correct measuring method for K will be describedlater.

[0066] The charging voltage Vs on the substrate surface during thetreatment may be reach several hundreds to about 1000V, unless theneutralization by electrons is made appropriately. To divide such highcharging voltage Vs into the measuring voltage Vm of about several voltssuitable for the measurement, it is preferred that the electrostaticcapacity Cm of the measuring capacitor 18 is decided so that the valueof K may be about 100 to 10000, or preferably about 1000. In the exampleas shown in FIG. 7, when the ion beam 2 mechanically scans the substrateholding unit 4 and the substrate 6, it is confirmed that the chargingvoltage Vs is varied over time. In such a case, to enhance themeasurement precision by extending the time constant of the measuringcircuit, it is preferred that the electrostatic capacity Cm of themeasuring capacitor 18 is decided to set the value of K to the abovevalue. This is especially preferable for the charging voltage measuringdevice 12 as shown in FIG. 3.

[0067] As described above, with this charging voltage measuring device12, there is no need for disposing the measuring electrode 8 on thesubstrate 6 in contrast to the related-art technique, and the measuringelectrode 14 that is not obstacle for treating the substrate 6 isemployed, whereby the charging voltage Vs on the surface of thesubstrate 6 during the actual treatment is measured in real time, asshown in FIG. 12.

[0068] And the charging voltage Vs on the surface of the substrate 6itself being actually treated is measured employing voltage dividingunit with two electrostatic capacities Cs and Cm in contract to therelated-art technique as shown in FIG. 12, whereby the charging voltageVs on the surface of the substrate 6 is accurately measured without riskthat the measurement precision is decreased due to a difference betweenthe surface materials.

[0069] By the way, in the charging voltage measuring device 12 as shownin FIG. 1, the internal resistor of the voltmeter 20 is sufficientlylarge, whereby it is ignored that charges on the surface of thesubstrate 6 leak into the ground potential portion via the internalresistor of the voltmeter 20 during the measurement. If the chargingvoltage Vs is corrected for the amount of charges, the measurementprecision of the charging voltage Vs on the substrate surface is furtherenhanced. An example of the charging voltage measuring device 12 will bepresented below.

[0070]FIG. 3 is a view showing a charging voltage measuring deviceaccording to another embodiment of the invention. FIG. 4 is anequivalent circuit diagram around the measuring capacitor in FIG. 3. Inthe following, the different points from the embodiment of FIGS. 1 and 2will be chiefly described.

[0071] In this charging voltage measuring device 12, the measuringresistor 24 is connected in parallel to the measuring capacitor 18.Assuming that the resistance value of the measuring resistor 24 is R2and the internal resistance value of the voltmeter 20 is R1, theresistance value Rm of a combination of both or the resistance value Rmof a resistor in parallel to the measuring capacitor 18 is representedin the following table.

Rm=R1−R2/(R1+R2)[Numerical expression 5]

[0072] The reason why the measuring resistor 24 is provided is that themeasurement precision of the charging voltage Vs is enhanced byclarifying the resistance value Rm of the resistor in parallel to themeasuring capacitor 18. Accordingly, when the internal resistance valueR1 of the voltmeter 20 is clear, it is unnecessary to provide themeasuring resistor 24. In this case, Rm is equal to R1. When themeasuring resistor 24 is provided, the resistance value R2 is preferablyfully smaller (about {fraction (1/10)}) than the internal resistancevalue R1 of the voltmeter 20. In this way, in the synthetic resistancevalue Rm, the clear resistance value R2 of the measuring resistor 24 ispredominant and less subject to influence of variations in the internalresistance value R1 of the voltmeter 20. If the resistance value R2 istoo small, the time constant of the measuring circuit is excessivelyreduced, so that the amount of charges incident on the substrate 6 andthus the charging voltage Vs are varied over time, the charging voltageVs is difficult to measure, whereby the resistance value R2 of themeasuring resistor 24 is preferably from several kΩ to several MΩ.

[0073] The resistance value Rm may be calculated within the calculator22, or by may be calculated in other ways and set in the calculator 22,whereby the calculator 22 makes the calculation in accordance with thenumerical expression 2. Thereby, the arithmetical operation of thecalculator 22 is simplified.

[0074] The voltmeter 20 always measures the measuring voltage Vm acrossthe measuring capacitor 18 during the measurement and passes it to thecalculator 22. The calculator 22 makes the following calculation. Thatis, assuming that the time is t, and the measuring voltage Vm isrepresented by Vm(t) as the function of time, when the measurement starttime is t=0, and arbitrary time (e.g., when the charging voltage Vs isdesired to know) during the measurement is t1, the charging voltage Vson the surface of the substrate 6 at arbitrary time t1 during treatmentand measurement is calculated in accordance with the numericalexpression 2 on the basis of the inverse K of the voltage dividingratio, the resistance value Rm and the measuring voltage Vm(t1) at timet1. The measurement start time may be the time when the surface of thesubstrate 6 is not electrified without mistake, and set to t=0. The unitin the numerical expression 2 is SI unit, and the unit of time issecond.

[0075] A portion of the first term Vm(t1) within large brackets in thenumerical expression 2 multiplied by K is almost the same content as inthe numerical expression 1. The concept of time is only considered.

[0076] The second term {1/(Cm·Rm)}∫₀ ^(t1)Vm(t)dt within the largebrackets in the numerical expression 2 is provided to correct for anamount of electrons on the substrate surface leaking into the groundpotential portion through the resistance value Rm during the measurementby converting it into the voltage.

[0077] Explaining in more detail, {Vm(t)/Rm}dt that is based on in thenumerical expression 2 is the amount of charges leaking through theresistance value Rm per unit time, in which the sum of charges from timet=0 to time t1 is (1/Rm)∫₀ ^(t1)Vm(t)dt and the charging voltage iscorrected for this value, thereby enhancing the measurement precision ofthe charging voltage Vs. The reason why the sum is multiplied by 1/Cm isthat the sum is converted into the voltage, employing the relation V=Q/C(Q is charge and C is electrostatic capacity) for the capacitor.

[0078] The voltage in the second term within the large brackets in thenumerical expression 2 is measured at the same location across themeasuring capacitor 18, and converted into the voltage on the surface ofthe substrate 6 by multiplying it by the inverse K of the voltagedividing ratio. By making this conversion, the charging voltage Vs onthe surface of the substrate 6 being actually treated is measured moreaccurately by correcting for an error due to charges leaking into theground potential portion via the resistance value Rm during themeasurement.

[0079] The inverse K of the voltage dividing ratio is calculated(actually measured) simply and correctly in the following way. The valueK varies depending on both a thickness of the substrate and a dielectricconstant of the substrate. Therefore, the value of K is determinedbefore irradiating an ion beam.

[0080] That is, a dummy electrode 26 for simulating the electrificationis placed closely on the surface of the substrate 6, a dummy voltage Vdfrom a dummy power source 28 is applied between it and the groundpotential portion to measure the measuring voltage Vm across themeasuring capacitor 18 using the voltmeter 20, as shown in FIG. 6. Anapparatus for irradiating the ion beam is exposed in the atmosphere whensimulating the electrification by using the dummy electrode 26.Therefore, the dummy electrode 26 does not prevent irradiating the ionbeam on the substrate. The dummy electrode 26 is a conductor plate suchas an aluminum foil. The dummy voltage Vd is preferably a sinusoidal ACvoltage. In this way, the dummy power source 28 is simplified, and thedummy voltage Vd is repeatedly applied, thereby producing a staterelatively close to the state where the substrate holding unit 4 and thesubstrate 6 are mechanically scanned by the ion beam 2. The dummyvoltage Vd is not necessarily the sinusoidal AC voltage, but only needsto have a portion where the value is varied over time. For example, a DCvoltage at a moment when it is applied, or a rectangular voltage may bepossible.

[0081] The dummy voltage Vd is applied on the surface of the substrate6, like the charging voltage Vs, to simulate the charging voltage Vs onthe substrate surface, wherein it is considered that Vd is equal to Vs.If this relation is substituted for the numerical expression 3 or 4, theinverse K of the voltage dividing ratio is obtained from the followingnumerical expression 6 or 7. In the charging voltage measuring device 12of FIG. 1 with the numerical expression 3, the numerical expression 6may be employed, while in the charging voltage measuring device 12 ofFIG. 3 with the numerical expression 4, the numerical expression 7 maybe employed. When the inverse K of the voltage dividing ratio in thenumerical expression 8 is employed, the measuring resistor 24 is notprovided.

K=Vd/Vm[Numerical expression 6]

K=Vd/[Vm(t1)+{1/(Cm·Rm)}∫₀ ^(t1) Vm(t)dt][Numerical expression 7]

[0082] The charging voltage measuring device 12 may be applied to othercases than where the substrate 6 is irradiated with the ion beam 2 forion implantation or ion doping. For example, the charging voltagemeasuring device 12 may be applied to the process or apparatus in whichthe surface of the substrate is possibly electrified such as the processor apparatus for making the plasma treatment on the substrate, orprocess or apparatus for conveying or drying the substrate.

[0083] An example of the ion beam irradiating device will be describedbelow, which includes the charging voltage measuring device 12 as shownin FIGS. 1 and 3 and makes the feedback control so that the chargingvoltage Vs on the substrate surface during the treatment that ismeasured by it falls within the reference voltage range.

[0084] This ion beam irradiating device radiates the ion beams 2 ontothe substrate 6 held on the substrate holding unit to make the ionimplantation or ion doping within the vacuum vessel 30.

[0085] The measuring electrode 14 constituting the charging voltagemeasuring device 12 is provided between the substrate holding unit 4 andthe substrate 6. Herein, the insulating layer 16 is not shown. Oneexample of the planar shape of this measuring electrode 14 is shown inFIG. 9. This is the same figure as FIG. 5. A portion of the measuringcapacitor 18, the voltmeter 20, the calculator 22 and the measuringresistor 24 is collectively shown as a circuit 17, from which thecharging voltage Vs measured in the above way is output. That is, thecharging voltage measuring device 12 is made up of the measuringelectrode 14 and the circuit 17.

[0086] In this example, the substrate holding unit 4, the substratemounted thereon and the measuring electrode 14 are mechanically driven(scanned) in the reciprocating motion in the X direction of the arrow bya driving device 32.

[0087] The ion beam 2 is not scanned in this example. The sectionalshape of this ion beam 2 is a rectangle that is longer in the Ydirection orthogonal to the X direction, and one example thereof isshown in FIG. 9. The width of the ion beam 2 in the X direction isactually slightly narrower, but shown widely. The ion beam 2 may bescanned in the form of spot in the Y direction.

[0088] A plasma generating device 34, as one example of the electronsupply source, for generating electrons, supplying them to the substrate6 and suppressing electrification on the substrate surface from beingcaused by the ion beam irradiation is provided near the substrateholding unit 4 and the substrate 6 upstream side thereof.

[0089] This plasma generating device 34 generates a plasma (naturallycontaining electrons) 40 by introducing a gas into a plasma generatingvessel 36, generating an arc discharge between a filament 38 and theplasma generating vessel 36, and ionizing the gas, and thereby suppliesthe plasma to the passage of the ion beam 2 to supply electrons in theplasma 40 along with the ion beam 2 to the substrate 7 to suppresselectrification on the substrate surface. The filament 38 is heated by avoltage variable filament power source 42. An arc discharge voltage froman arc power source 44 is applied between the filament 38 and the plasmagenerating vessel 36. An extraction voltage for facilitating theextraction of plasma is applied from an extraction power source 46between the plasma generating vessel 36 and a beam line tube 31 leadingto the vacuum vessel 30.

[0090] Moreover, this ion beam irradiating device includes a controllerfor maintaining the amount of plasma 40 generated from the plasmagenerating device 34, when the charging voltage Vs is within a referencevoltage range RV, increasing the amount of plasma 40 generated from theplasma generating device 34 when it is higher than the reference voltagerange RV, or decreasing the amount of plasma 40 generated from theplasma generating device 34 when it is lower than the reference voltagerange RV on the basis of the charging voltage Vs of the substratemeasured by the charging voltage measuring device 12.

[0091] When the amount of plasma 40 generated from the plasma generatingdevice 34 is increased, an upward instruction signal UP is supplied fromthe controller 48 to the filament power source 42 to increase its outputvoltage. As a result, the filament current, the amount of dischargeelectrons from the filament 38, the arc discharge current, and theamount of generating the plasma 40 are increased. When the amount ofplasma 40 generated from the plasma generating device 34 is decreased,an downward instruction signal DN is supplied from the controller 48 tothe filament power source 42 to increase its output voltage. As aresult, owing to an opposite action, the amount of generating the plasma40 is decreased. When the amount of plasma 40 generated from the plasmagenerating device 34 is maintained, neither the upward instructionsignal UP nor the downward instruction signal DN are supplied to thefilament power source 42.

[0092] A specific example of the controller 48 is shown in FIG. 8. Thiscontroller 48 has a comparator 50 in which the upper limit value RV1 inthe reference voltage range RV is set as the reference value, and acomparator 52 in which the lower limit value RV2 in the referencevoltage range RV is set as the reference value. Both the comparators 50and 52 are supplied with the charging voltage Vs as the comparisonobject from the charging voltage measuring device 12. When the chargingvoltage Vs is higher than the upper limit value RV1, the upwardinstruction signal UP is output from the comparator 50. When thecharging voltage Vs is lower than the lower limit value RV2, thedownward instruction signal DN is output from the comparator 52. Whenthe charging voltage Vs lies between the upper limit value RV1 and thelower limit value RV2, neither the signal UP nor DN are output.

[0093] It is the concept including the polarity ± of the chargingvoltage Vs that the charging voltage Vs measured by the charging voltagemeasuring device 12 is higher or lower than the reference voltage rangeRV. For example, when the reference voltage range RV is −3≦RV≦+3 [V],(a) the amount of generating the plasma 40 is maintained if the chargingvoltage Vs is within this range, and (b) the amount of generating theplasma 40 is increased if the charging voltage Vs is higher than +3V,for example, +6V. Thereby, in the plasma 40 supplied to the substrate 6,the amount of electrons is increased so that a positive charge up on thesubstrate surface is decreased the absolute value of the chargingvoltage Vs is reduced. Moreover, (c) the amount of generating the plasma40 is decreased if the charging voltage Vs is lower than −3V, forexample, −6V. Thereby, the plasma 40 supplied to the substrate 6 or theamount of electrons is decreased, so that a negative charge up on thesubstrate surface is decreased and the absolute value of the chargingvoltage Vs is reduced.

[0094] Because this ion beam irradiating device has the charging voltagemeasuring device 12, the charging voltage Vs on the substrate surfacebeing actually treated is accurately measured.

[0095] Additionally, since the controller 48 makes the feedback controlto the plasma generating device 34, the charging voltage Vs on thesubstrate surface being treated is automatically controlled to be withinthe reference voltage range RV.

[0096] For the electron supply source for suppressing theelectrification, an electron generating device for generating electronsalone for supply to the substrate 6 or the ion beam 2 may be employed,instead of the plasma generating device 34 for generating the plasma 40containing electrons.

[0097] The measuring electrode 14 constituting the charging voltagemeasuring device 12 in each embodiment is not limited to one sheet, butmay be a plurality of sheets, each sheet being provided with themeasuring capacitor 18 (the measuring resistor 24, as needed), themeasuring voltage Vm across the measuring capacitor 18 is measured, thecharging voltage Vs on the substrate surface at multiple locationscorresponding to the measuring electrodes 14 may be measured bycalculation in accordance with the numerical expression 3 or 4,employing the measured voltage Vm. In this way, the distribution ofcharging voltage Vs on the substrate surface is also measured. Tomeasure the measuring voltage Vm at multiple locations, a data loggerfor measuring the voltage at a plurality of locations may be employed,instead of a plurality of voltmeters 20.

[0098] For example, when the substrate holding unit is mechanicallyscanned in the X direction, a plurality of measuring electrodes 14 maybe disposed in the X direction in the example as shown in FIG. 10. Inthis way, the distribution of charging voltage Vs on the substratesurface in the X direction is measured. In this case, each measuringelectrode 14 is preferably a width equal or slightly smaller than thatof the ion beam 2 in the X direction.

[0099] Moreover, a plurality of measuring electrodes 14 may be disposedin the Y direction in the example as shown in FIG. 11. In this way, thedistribution of charging voltage Vs on the substrate surface in the Ydirection can be measured.

[0100] In the case wherein the plurality of measuring electrode 14 areprovided to measure the charging voltage Vs at the plurality oflocations, the electron supply source (e.g., plasma generating device34) is controlled so that the maximum absolute value of charging voltageVs at the plurality of locations may fall within the reference voltagerange RV.

[0101] Also, this invention is applied to the case where an ionizer isemployed to generate the positive and negative ions for supply to thesubstrate 6. This ionizer is employed to suppress the electrification ofthe substrate surface, when the substrate 6 is conveyed or dried in theatmosphere. In this case, the charging voltage measuring device 12 maybe constituted by providing the measuring electrode 14 on the substrateholding unit 4 for conveying or drying the substrate 6. Moreover,employing the charging voltage Vs on the substrate surface that ismeasured by the charging voltage measuring device 12, the ionizer issubjected to the feedback control so that the charging voltage Vs mayfall within the reference voltage range by changing the percentage ofpositive ions to negative ions that are generated from the ionizer onthe basis of the same idea of the embodiment as shown in FIG. 7.

EFFECT OF THE INVENTION

[0102] This invention is constituted in the above way and has thefollowing effects.

[0103] According to the first aspect of the invention, since themeasuring electrode that is not an obstacle for treatment of thesubstrate is employed, the charging voltage on the surface of thesubstrate being actually treated can be measured in real time. Inaddition, the charging voltage on the surface of the substrate itself tobe actually treated is measured employing voltage dividing unit with twoelectrostatic capacities, whereby the charging voltage on the substratesurface is accurately measured.

[0104] According to second aspect of the invention, since the measuringelectrode that is not an obstacle for treatment of the substrate isemployed, the charging voltage on the surface of the substrate beingactually treated can be measured in real time. In addition, the voltageis corrected for an amount of charges on the substrate surface leakingthrough the resistor in parallel to the measuring capacitor such as theinternal resistor of the voltmeter into the ground potential portionduring the measurement by converting it into the voltage on thesubstrate surface, whereby the charging voltage on the substrate surfacebeing actually treated is accurately measured by correcting for an errordue to the leakage.

[0105] According to third aspect of the invention, since the chargingvoltage measuring device according to first or second aspect of theinvention is provided, the charging voltage on the substrate surfacebeing actually treated is accurately measured. Additionally, thecontroller is provided to make the feedback control for the electrondischarge source to automatically control the charging voltage on thesubstrate surface being actually treated to fall within the referencevoltage range.

What is claimed is:
 1. A charging voltage measuring apparatus formeasuring a charging voltage Vs on the surface of a substrate on asubstrate holding unit, comprising: a measuring electrode, for formingan electrostatic capacity Cs with said substrate, being disposed on saidsubstrate holding unit to make contact with or proximate to the backface of said held substrate, and said measuring electrode beingelectrically insulated from said substrate holding unit; a measuringcapacitor connected between said measuring electrode and a groundpotential portion, said measuring capacitor having an electrostaticcapacity Cm; a voltage measuring unit for measuring a measuring voltageVm between both ends of said measuring capacitor; and a calculating unitfor calculating said charging voltage Vs in accordance with a followingnumerical expression 1 or its mathematically equivalent numericalexpression on the basis of an inverse K of a voltage dividing ratio thatis defined by the relation of said electrostatic capacities Cs and Cmand said measuring voltage Vm. Vs=K×Vm[Numerical expression 1] whereK=(Cs+Cm)/Cs or K=Cm/Cs (if Cm>>Cs)
 2. A charging voltage measuringdevice apparatus for measuring a charging voltage Vs on the surface of asubstrate held on a substrate holding unit, comprising: a measuringelectrode, for forming an electrostatic capacity Cs with said substrate,being disposed on said substrate holding unit to make contact with orproximate to the back face of said held substrate, and said measuringelectrode being electrically insulated from said substrate holding unit;a measuring capacitor connected between said measuring electrode and aground potential portion, said measuring capacitor having anelectrostatic capacity Cm; a voltage measuring unit for measuring ameasuring voltage Vm between both ends of said measuring capacitor; anda calculator calculating unit for calculating said charging voltage Vsat time t1 in accordance with a following numerical expression 2 or itsmathematically equivalent numerical expression on the basis of aninverse K of a voltage dividing ratio that is defined by the relationbetween said electrostatic capacities Cs and Cm, and said measuringvoltage Vm(t1) at time t1, and a resistance value Rm of a resistorincluding an internal resistor of said voltmeter and disposed inparallel to said measuring capacitor, when the time is t, themeasurement start time is t=0, and the measurement time is t1.Vs=K[Vm(t1)+{1/(Cm×Rm)}ò0t1Vm(t)dt][Numerical expression 2] whereK=(Cs+Cm)/Cs or K=Cm/Cs (if Cm>>Cs)
 3. An ion beam irradiating deviceapparatus for irradiating an ion beam onto a substrate held on asubstrate holding unit, comprising: an plasma generating source forgenerating and supplying electrons to said substrate to suppress theelectrification on the surface of said substrate caused by irradiatingsaid ion beam; a charging voltage measuring device for the substrateaccording to claim 1; and a controller unit for controlling an amount ofelectrons generated from said electron supply source on the basis ofcharging voltage Vs measured by said charging voltage measuring device;wherein said control unit controls to maintain said amount of saidelectrons generated from said electron supply source when said chargingvoltage Vs is within a reference voltage range, wherein said controlunit controls to increase said amount of said electrons generated fromsaid electron supply source when said charging voltage Vs is higher thansaid reference voltage range, and wherein said control unit controls todecrease said amount of said electrons generated from said electronsupply source when said charging voltage Vs is lower than said referencevoltage range.
 4. An ion beam irradiating apparatus for irradiating anion beam onto a substrate held on a substrate holding unit, comprising:an plasma generating source for generating and supplying electrons tosaid substrate to suppress the electrification on the surface of saidsubstrate caused by irradiating said ion beam; a charging voltagemeasuring device for the substrate according to claim 2; and a controlunit for controlling an amount of electrons generated from said electronsupply source on the basis of charging voltage Vs measured by saidcharging voltage measuring device; wherein said control unit controls tomaintain said amount of said electrons generated from said electronsupply source when said charging voltage Vs is within a referencevoltage range, wherein said control unit controls to increase saidamount of said electrons generated from said electron supply source whensaid charging voltage Vs is higher than said reference voltage range,and wherein said control unit controls to decrease said amount of saidelectrons generated from said electron supply source when said chargingvoltage Vs is lower than said reference voltage range.
 5. The chargingvoltage measuring device according to claim 1, wherein said measuringelectrode is a conductive plate covered with an insulating layer.
 6. Thecharging voltage measuring device according to claim 2, wherein saidmeasuring electrode is a conductive plate covered with an insulatinglayer.